1. Field of the Invention
The present invention relates to radios and global positioning system (GPS) receivers. Moore particularly, the invention relates to a combined GPS receiver and radio unit operable for sending and receiving GPS-derived location data and other information and for providing tracking information that permits a user to follow or go to another user.
2. Description of the Prior Art
The global positioning system (GPS) is an electronic satellite navigation system which permits users to determine their position with respect to the Earth. Global positioning may be determined with a handheld GPS receiver which detects and decodes signals from a number of satellites orbiting the Earth. The signals from each of these satellites indicate the position of the satellite and the time at which the signals were sent. To decode the satellite signals, known as spread spectrum signals, and thereby calculate desired position and navigational data, a GPS receiver must first “find” or acquire the signals emitted from a minimum number of satellites. Once the receiver is “locked on” to the spread spectrum signals, the user's global position and other navigational data (e.g., velocity of movement) can be calculated.
In addition to the growing popularity and demand for GPS navigational devices, portable two-way radios continue to enjoy widespread popularity. In 1996, the Federal Communications Commission (FCC) established the Family Radio Service (FRS) so that families and other small groups could communicate with one another over very short distances (typically less than two miles) at no charge and without an FCC license. The FRS, which is one of the Citizens Band Radio Services, includes 14 channels in the UHF 465 MHz band. There are a number of commercially available two-way radios which are designed for use with the FRS.
The increasing use of both portable radios and GPS receivers has led to proposals to incorporate the two into combined units. It is anticipated that such combined units will provide enhanced capabilities such as the ability to transmit GPS-derived location data between two or more units so that the users of the units may monitor each other's location. For example, a family may use several of these combined units to not only communicate with one another but also to monitor each other's location so that parents may keep track of their children.
Unfortunately, currently-proposed combined GPS/radio units and GPS receivers in general suffer from several limitations that limit their utility. For example, although current GPS receivers are operable for determining their own locations and for providing directions or proposed routes to fixed locations, they are not operable for providing directions or proposed routes to moving waypoints such as other portable GPS units whose locations frequently change. This is a problem because GPS users often desire continuous navigation information on a moving target. For example, a driver of a vehicle equipped with a GPS unit may wish to follow or go to a driver of another moving vehicle equipped with a GPS unit or a hiker carrying a portable GPS unit may wish to follow or go to another hiker carrying a portable GPS unit.